Abstract <p>The behavior of a representative series of previously unknown 2-(alkylsulfanyl)quinolines, prepared from aryl isothiocyanates, allene or acetylene carbanions, and methyl iodide, under electron ionization (70 eV) have been studied for the first time. The studied compounds all form stable molecular ions clearly detected in the mass spectra and have similar fragmentation patterns, including the formation of [<i>M</i> – H]⁺, [<i>M</i> – Me]⁺, and [<i>M</i> – HS]⁺ ions. Fragmentation is most affected by the nature of the substituents in positions 3 and 4 of the quinoline pyridine ring. The molecular ion of 4-methyl-2-(methylsulfanyl)-3-(1<i>H</i>-pyrrol-1-yl)quinolines undergoes rearrangement, which involves either the sulfur atom or the carbon atom of the 4-methyl substituent in the heteroring. The fragmentation pathways of the fragment ions of the studied 2-(alkylsulfanyl)quinolines are proposed based on an analysis of the daughter ion mass spectra.</p>